1. Field of the Invention
The present invention relates to a universal serial bus (USB), and more particularly, to a USB with a power-saving mode and an operating method thereof.
2. Description of the Related Art
Universal serial bus (USB) technology has been widely used to various peripheral devices. With the development of electronics technology, the USB standard has been upgraded from USB1.1 to USB2.0. The data transmission speed has also increased from 12 Mbps to 480 Mbps.
The high-speed USB2.0 has surpassed the transmission speed of the USB1.1 by 40 times, and the USB2.0 has more application on various products. Usually, low-speed transmission devices, such as keyboards or mouse, use USB1.1 for data transmission. Since the speed of the USB2.0 has been greatly improved, it can be like the Fire Wire/IEEE 1394, and have wide applications on those devices needing large broad band, such as digital cameras, video cameras, storage apparatus, scanners and so on. In addition, the USB2.0 has other advantages that Fire Wire/IEEE 1394 does not have. For example, the USB has the feature of plug-and-play, which is suitable for personal digital assistants (PDAs), digital cameras, MP3 players or other portable devices. However, these portable devices are usually powered by batteries. How to reduce power consumption when operating the USB is a task to be dealt with for portable devices.
FIGS. 1-3 are schematic drawings showing conventional USB devices. Referring to FIG. 1, the USB2.0 host 110 is directly coupled to the USB2.0 peripheral 120 via connecting terminals. Since the USB2.0 host 110 and the USB2.0 peripheral 120 support high-speed data transmission, the data transmission speed can be 480 Mbps.
Referring to FIG. 2, the USB2.0 host 210 is coupled to the USB2.0 peripheral 220 via the hub 215. Since the USB2.0 host 210, the hub 215 and the USB2.0 peripheral 220 support high-speed data transmission, the data transmission speed can be 480 Mbps.
With reference to FIG. 3, the USB2.0 host 310 is directly coupled to the USB2.0 peripheral 320 via connecting terminals. Since the USB2.0 host 310 does not support high-speed transmission, the data transmission speed can only be 12 Mbps. It is called full-speed transmission or 1.5 Mbps low-speed transmission.
For desk-top computers, the application of USB2.0 for data transmission does not affect the operations even if the high-speed data transmission consumes a huge amount of power. For PDAs, digital cameras, MP3 players or the other portable devices which are powered by batteries, however, the high-speed data transmission can easily exhaust the batteries and reduce the operation time.